1. Field of the Invention
The present invention relates to a method and related apparatus for a user equipment improving continuous packet connectivity (CPC) in a wireless communications system, and more particularly, to a method and related apparatus for a user equipment improving configurations of an HS-SCCH less operation of CPC in a wireless communications system.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast and instantaneous transmission. Thus, targeting at the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate. For HSDPA and HSUPA, the 3rd Generation Partnership Project (3GPP) provides a Continuous Packet Connectivity (CPC) protocol specification, which includes features that, for user equipments (UEs) in CELL_DCH state, aim to significantly increase the number of packet data users for a cell, reduce the uplink noise rise and improve the achievable download capacity for VoIP.
For an HSDPA UE, physical channels include a high speed physical downlink shared channel (HS-PDSCH), for transferring payload data, and a high speed physical control channel (HS-DPCCH) for uploading an acknowledgement/negative acknowledgement (ACK/NACK) and a channel quality identifier (CQI). As for the media access control (MAC) layer of the HSDPA UE, a MAC-hs entity utilizes High Speed Downlink Shared Channel (HS-DSCH) for receiving data from the physical layer. In addition, Shared Control Channel for HS-DSCH (HS-SCCH) is a physical downlink channel, responsible for transmission of control signals corresponding to HS-DSCH, such as demodulation information.
CPC includes an HS-SCCH less operation, which is a special mode of HSDPA operation for reducing HS-SCCH overhead of a hybrid automatic repeat request (HARQ) process, thereby reducing UE power consumption. Under this mode, a first HS-DSCH transmission of the HARQ process corresponding to a transport block (TB) on pre-defined HS-DSCH is performed without accompaniment of HS-SCCH signaling. In this case, the UE needs to perform blind decoding for obtaining TB data of the first transmission based on predefined TB size and channel coding set. If the TB data is decoded successfully, the UE reports a positive acknowledgement (ACK) to the base station, also known as Node-B, through the HS-SCCH; otherwise, the UE does not report any signal and waits for retransmission initiated by the Node-B. Note that, in the HS-SCCH less operation, HARQ retransmissions corresponding to the first HS-DSCH transmission are restricted to two times. Moreover, when performing the HARQ retransmission, the network will transmit required control signals such as “UE identity”, “physical channel coding set”, “TB size”, “pointer”, etc. through the HS-SCCH, and the UE can then report ACK or NACK for the retransmission for properly terminating the HARQ process.
As to radio resource control (RRC), the UE and the network, such as the Node-B or a radio network controller (RNC), can configure CPC by exchanging RRC messages and information elements (IEs) that include corresponding parameters. According to the RRC protocol specification of 3GPP, an IE “Continuous Packet Connectivity HS-SCCH Less Information” is provided by the network to inform the UE of required configuration and parameters before enabling the HS-SCCH less operation, among which a variable “HS-PDSCH Code Index” is utilized for configuring a first HS-PDSCH code of the UE, a variable “Transport Block Size List” is utilized for informing the UE of an TB size list including indexes of TB sizes possibly transmitted by the network, an variable “Transport Block Size Index” is utilized for indicating the TB sizes corresponding to each TB size index in the variable “Transport Block Size List” and a variable “HS-PDSCH Second Code Support” is utilized for indicating whether a second HS-PDSCH code is needed to support TB reception for each TB size listed in the variable “Transport Block Size List”. If any TB sizes in the variable “Transport Block Size List” need support of the second HS-PDSCH code, which is configured by the network, a variable “HS-PDSCH Second Code Index” is further included for configuring the second HS-PDSCH code of the UE.
That means, for each TB size listed in the variable “Transport Block Size List”, the UE can determine whether the second HS-PDSCH code is used for supporting TB reception according to the variable “HS-PDSCH Second Code Support”, so that TB data can be obtained from the HS-PDSCH by simultaneously using the first and second HS-PDSCH code.
As well-known by those skilled in the art, the HS-PDSCH has 16 channel codes (or called spreading factors). Thus, the prior art has to use 4 bits (i.e. the variable “HS-PDSCH Code Index”) for indicating which code in an Orthogonal Variable Spreading Factor (OVSF) code tree is the first HS-PDSCH code, and use the other 4 bits (i.e. the variable “HS-PDSCH Second Code Index) for indicating the second HS-PDSCH code. In this case, except the 4 bits for indicating the first HS-PDSCH code, if the second HS-PDSCH code is needed for supporting TB reception at this time, the network has to transmit the other 4 bits for configuring the second HS-PDSCH code, resulting in the waste of system radio resources.